As shown in, for example, FIG. 10, an exhaust manifold 1 attached to a side surface of an engine 2 vibrates itself and generates a vibrant because combustion exhaust gas of which pressure or temperature pulsates passes inside the exhaust manifold 1 when the engine is driven. The exhaust manifold 1 is heated by the combustion exhaust gas having a high temperature which passes inside the exhaust manifold 1 and thus generates heat itself. In order to suppress the vibrant or the heat generated in this manner by the exhaust manifold 1 from being transmitted to an area around the engine 2, a heat insulator 3 is attached so as to cover the exhaust manifold 1.
However, when the heat insulator 3 is directly attached to the vibrating exhausting manifold 1 or engine 2, there is an undesirable possibility that the heat insulator 3 resonates to become a vibration source itself and thus enlarges the noise.
Under these circumstances, Patent Document 1 proposes a cushioning device 5 having a floating mount structure (see FIG. 15) for attaching a heat insulator 3 to the exhaust manifold 1 of the engine 2 as described above. FIG. 15 is a cross-sectional view of the cushioning device 5 proposed in Patent document 1 specified below.
The cushioning device 5 of the conventional art includes an annular cushioning member 8 formed by knitting metal fibers into a mesh and putting the resultant metal fiber mesh into a planar mat-like shape, a grommet 20 which is a coupling member formed of an aluminum alloy and having a generally S-shaped cross-section, and a collar member 10 located between the cushioning member 8 and an attaching bolt 42.
Between the collar member 10 and the cushioning member 8, a gap 17 is formed in an axial direction and in a radial direction of the attaching bolt 42. It is described in Patent Document 1 that owing to the gap 17, the vibration input from the exhaust manifold 1 is suppressed from being transmitted from the collar member 10 to the cushioning member 8; namely, the cushioning device 5 has a superb vibration-damping property.
In more detail, Patent Document 1 describes as follows. The vibration transmitted from the collar member 10 to the cushioning member 8 causes the cushioning member 8 itself to make a flexural motion. Owing this flexural motion, the cushioning device 5 converts the vibration energy of the vibration transmitted from the collar member 10 into a kinetic energy of the flexure of the cushioning member 8 and thus can suppress the vibration from being transmitted to the heat insulator 3.
However, since the gap 17 in which the cushioning member 8 is loosely movable inside the collar member 10 is provided between the collar member 10 and the cushioning member 8, the cushioning member 8 vibrates inside the collar member 10 and thus collides against the collar member 10. The collision of the cushioning member 8 against and the collar member 10 may undesirably generate a rattling noise. Namely, the gap 17 provided for suppressing the vibration from being transmitted from the collar member 10 to the cushioning member 8 acts as a play between the collar member 10 and the cushioning member 8 to generate a different type of noise. Generation of such a different type of noise is considered to mean that another vibration is generated, which inhibits the vibration-damping property.